Power generation system exhaust cooling

ABSTRACT

An airflow control system for a gas turbine according to an embodiment includes: an airflow generation system for attachment to a rotatable shaft of a gas turbine system, the airflow generation system drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream of the gas turbine system; an air extraction system for: extracting at least a portion of the excess flow of air generated by the airflow generation system to provide bypass air; and diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream; and an exhaust processing system for processing the reduced temperature exhaust gas stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. application numbers: ______, GE docket numbers 280650-1, 280687-1, 280688-1, 280692-1, 280707-1, 280714-1, 280730-1, 280731-1, 280815-1, 281003-1, 281004-1, 281005-1 and 281007-1 all filed on ______.

BACKGROUND OF THE INVENTION

The disclosure relates generally to power generation systems, and more particularly, to systems for cooling the exhaust gas of power generation systems.

Exhaust gas from power generation systems, for example a simple cycle gas turbine power generation system, often must meet stringent regulatory requirements for the composition of the exhaust gas released into the atmosphere. One of the components typically found in the exhaust gas of a gas turbine power generation system and subject to regulation is nitrogen oxide (i.e., NO_(x)), which includes, for example, nitric oxide and nitrogen dioxide. To remove the NO_(x) from the exhaust gas stream, technology such as selective catalytic reduction (SCR) is often utilized. In an SCR process, ammonia (NH₃) or the like reacts with the NO_(x) and produces nitrogen (N₂) and water (H₂O).

The effectiveness of the SCR process depends in part on the temperature of the exhaust gas that is processed. The temperature of the exhaust gas from a gas turbine power generation system is often higher than about 1100° F. However, SCR catalysts need to operate at less than about 900° F. to maintain effectiveness over a reasonable catalyst lifespan. To this extent, the exhaust gas from a simple cycle gas turbine power generation system is typically cooled prior to SCR.

Large external blower systems have been used to reduce the exhaust gas temperature of a gas turbine power generation system below 900° F. by mixing a cooling gas, such as ambient air, with the exhaust gas. Because of the possibility of catalyst damage due to a failure of an external blower system, a redundant external blower system is typically utilized. These external blower systems include many components, such as blowers, motors, filters, air intake structures, and large ducts, which are expensive, bulky, and add to the operating cost of a gas turbine power generation system. Additionally, the external blower systems and the operation of the gas turbine power generation system are not inherently coupled, thus increasing the probability of SCR catalyst damage due to excess temperature during various modes of gas turbine operation. To prevent SCR catalyst damage due to excess temperature (e.g., if the external blower system(s) fail or cannot sufficiently cool the exhaust gas), the gas turbine may need to be shut down until the temperature issue can be rectified.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides an airflow control system for a gas turbine system, including: an airflow generation system for attachment to a rotatable shaft of a gas turbine system, the airflow generation system drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream of the gas turbine system; and an air extraction system for extracting at least a portion of the excess flow of air generated by the airflow generation system to provide bypass air, and for diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream.

A second aspect of the disclosure provides a turbomachine system, including: a gas turbine system including a compressor component, a combustor component, and a turbine component; a shaft driven by the turbine component; a fan coupled to the shaft upstream of the gas turbine system for drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream produced by the gas turbine system; an air extraction system for: extracting at least a portion of the excess flow of air generated by the can to provide bypass air; and diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream; an airflow controller for controlling the air extraction system to maintain the reduced temperature exhaust gas stream at a temperature of less than about 900° F.; and a selective catalytic reduction (SCR) system for processing the reduced temperature exhaust gas stream.

A third aspect of the disclosure provides a power generation system, including: a gas turbine system including a compressor component, a combustor component, and a turbine component; a shaft driven by the turbine component; an electrical generator coupled to the shaft for generating electricity; a fan coupled to the shaft upstream of the gas turbine system for drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream produced by the gas turbine system; an air extraction system for: extracting at least a portion of the excess flow of air generated by the can to provide bypass air; and diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream; an airflow controller for controlling the air extraction system to maintain the reduced temperature exhaust gas stream at a temperature of less than about 900° F.; and a selective catalytic reduction (SCR) system for processing the reduced temperature exhaust gas stream.

The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawing that depicts various embodiments of the disclosure.

FIG. 1 shows a schematic diagram of a simple cycle gas turbine power generation system according to embodiments.

FIG. 2 depicts an airflow generation system according to embodiments.

FIG. 3 depicts an enlarged view of a portion of the gas turbine power generation system of FIG. 1 according to embodiments.

FIG. 4 is a chart showing an illustrative relationship between the flow of bypass air into a mixing area and the temperature of the exhaust gas stream at different load percentages of a gas turbine system, according to embodiments.

It is noted that the drawing of the disclosure is not to scale. The drawing is intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawing, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, the disclosure relates generally to power generation systems, and more particularly, to systems and methods for cooling the exhaust gas of power generation systems.

FIG. 1 is a block diagram of a turbomachine system (e.g., a simple cycle gas turbine power generation system 10) that includes a gas turbine system 12 and an exhaust processing system 14. The gas turbine system 12 may combust liquid or gas fuel, such as natural gas and/or a hydrogen-rich synthetic gas, to generate hot combustion gases to drive the gas turbine system 12.

The gas turbine system 12 includes an air intake section 16, a compressor component 18, a combustor component 20, and a turbine component 22. The turbine component 22 is drivingly coupled to the compressor component 18 via a shaft 24. In operation, air (e.g., ambient air) enters the gas turbine system 12 through the air intake section 16 (indicated by arrow 26) and is pressurized in the compressor component 18. The compressor component 18 includes at least one stage including a plurality of compressor blades coupled to the shaft 24. Rotation of the shaft 24 causes a corresponding rotation of the compressor blades, thereby drawing air into the compressor component 18 via the air intake section 16 and compressing the air prior to entry into the combustor component 20.

The combustor component 20 may include one or more combustors. In embodiments, a plurality of combustors are disposed in the combustor component 20 at multiple circumferential positions in a generally circular or annular configuration about the shaft 24. As compressed air exits the compressor component 18 and enters the combustor component 20, the compressed air is mixed with fuel for combustion within the combustor(s). For example, the combustor(s) may include one or more fuel nozzles that are configured to inject a fuel-air mixture into the combustor(s) in a suitable ratio for combustion, emissions control, fuel consumption, power output, and so forth. Combustion of the fuel-air mixture generates hot pressurized exhaust gases, which may then be utilized to drive one or more turbine stages (each having a plurality of turbine blades) within the turbine component 22.

In operation, the combustion gases flowing into and through the turbine component 22 flow against and between the turbine blades, thereby driving the turbine blades and, thus, the shaft 24 into rotation. In the turbine component 22, the energy of the combustion gases is converted into work, some of which is used to drive the compressor component 18 through the rotating shaft 24, with the remainder available for useful work to drive a load such as, but not limited to, an electrical generator 28 for producing electricity, and/or another turbine.

The combustion gases that flow through the turbine component 22 exit the downstream end 30 of the turbine component 22 as a stream of exhaust gas 32. The exhaust gas stream 32 may continue to flow in a downstream direction 34 towards the exhaust processing system 14. The downstream end 30 of the turbine component 22 may be fluidly coupled via a mixing area 33 to a CO removal system (including, e.g., a CO catalyst 36) and an SCR system (including, e.g., an SCR catalyst 38) of the exhaust processing system 14. As discussed above, as a result of the combustion process, the exhaust gas stream 32 may include certain byproducts, such as nitrogen oxides (NO_(x)), sulfur oxides (SO_(x)), carbon oxides (CO_(x)), and unburned hydrocarbons. Due to certain regulatory requirements, an exhaust processing system 14 may be employed to reduce or substantially minimize the concentration of such byproducts prior to atmospheric release.

One technique for removing or reducing the amount of NO_(x) in the exhaust gas stream 32 is by using a selective catalytic reduction (SCR) process. For example, in an SCR process for removing NO_(x) from the exhaust gas stream 32, ammonia (NH₃) or other suitable reductant may be injected into the exhaust gas stream 32. The ammonia reacts with the NO_(x) to produce nitrogen (N₂) and water (H₂O).

As shown in FIG. 1, an ammonia evaporator system 40 and an ammonia injection grid 42 may be used to vaporize and inject an ammonia solution (e.g., stored in a tank 46) into the exhaust gas stream 32 upstream of the SCR catalyst 38. The ammonia injection grid 42 may include, for example, a network of pipes with openings/nozzles for injecting vaporized ammonia into the exhaust gas stream 32. As will be appreciated, the ammonia and NO_(x) in the exhaust gas stream 32 react as they pass through the SCR catalyst 38 to produce nitrogen (N₂) and water (H₂O), thus removing NO_(x) from the exhaust gas stream 32. The resulting emissions may be released into the atmosphere through a stack 44 of the gas turbine system 12.

The ammonia evaporator system 40 may further include, for example, a blower system 48, one or more heaters 50 (e.g., electric heaters), and an ammonia vaporizer 52, for providing vaporized ammonia that is injected into the exhaust gas stream 32 via the ammonia injection grid 42. The ammonia may be pumped from the tank 46 to the ammonia vaporizer 52 using a pump system 54. The blower system 48 may include redundant blowers, while the pump system 54 may include redundant pumps to ensure continued operation of the ammonia evaporator system 40 in case of individual blower/pump failure.

The effectiveness of the SCR process depends in part on the temperature of the exhaust gas stream 32 that is processed. The temperature of the exhaust gas stream 32 generated by the gas turbine system 12 is often higher than about 1100° F. However, the SCR catalyst 38 typically needs to operate at temperatures less than about 900° F.

According to embodiments, an airflow generation system 56 may be used to provide cooling air for lowering the temperature of the exhaust gas stream 32 to a level suitable for the SCR catalyst 38. As depicted in FIG. 1, the airflow generation system 56 may include a fan 58. The fan 58 may be coupled to the shaft 24 of the gas turbine system 12 upstream of the gas turbine system 12 to provide cooling air (e.g., ambient air) drawn in through the air intake section 16 that may be used to lower the temperature of the exhaust gas stream 32. The fan 58 may be fixedly mounted (e.g. bolted, welded, etc.) to the shaft 24 of the gas turbine system 12 using a mounting system 60. To this extent, the fan 58 is configured to rotate at the same rotational speed as the shaft 24. In other embodiments, as shown in FIG. 2, a clutch mechanism 62 may used to releasably couple the fan 58 to the shaft 24 of the gas turbine system 12. This allows the fan 58 to be selectively decoupled from the shaft 24 if not needed. When the clutch mechanism 62 is engaged, the fan 58 is coupled to the shaft 24 and is configured to rotate at the same rotational speed as the shaft 24. Clutch coupling/decoupling commands may be provided to the clutch mechanism 62 via an airflow controller 100 (FIG. 1). An adjustable speed drive system may also be used to couple the fan 58 to the shaft 24 to allow the fan 58 to be rotated at a different speed than the shaft 24.

The compressor component 18 has a flow rate capacity and is configured to draw in a flow of air (e.g., ambient air) via the air intake section 16 based on its flow rate capacity. In operation, the fan 58 is designed to draw in an additional flow of air through the air intake section 16 that is about 10% to about 40% of the flow rate capacity of the compressor component 18. In general, the percentage increase in the flow of air may be varied and selectively controlled based on several factors including the load on the gas turbine system 12, the temperature of the air being drawn into the gas turbine system 12, the temperature of the exhaust gas stream 32 at the SCR catalyst 38, etc.

As depicted in FIG. 3, an inlet guide vane assembly including a plurality of inlet guide vanes 66 may be used to control the amount of air directed toward and through the fan 58. Each inlet guide vane 66 may be selectively controlled (e.g., rotated) by an independent actuator 68. Actuators 68 according to various embodiments are shown schematically in FIG. 3, but any known actuator may be utilized. For example, the actuators 68 may comprise an electro-mechanical motor, or any other type of suitable actuator.

The actuators 68 may be independently and/or collectively controlled in response to commands from the airflow controller 100 to selectively vary the positioning of the inlet guide vanes 66. That is, the inlet guide vanes 66 may be selectively rotated about a pivot axis by the actuators 68. In embodiments, each inlet guide vane 66 may be individually pivoted independently of any other inlet guide vane 66. In other embodiments, groups of inlet guide vanes 66 may be pivoted independently of other groups of inlet guide vanes 66 (i.e., pivoted in groups of two or more such that every inlet guide vane 66 in a group rotates together the same amount). Position information (e.g., as sensed by electro-mechanical sensors or the like) for each of the inlet guide vanes 66 may be provided to the airflow controller 100.

The increased flow of air provided by the fan 58 may increase the air pressure at the compressor component 18. For example, in the case where the flow of air is increased from about 10% to about 40% by the operation of the fan 58, a corresponding pressure increase of about 5 to about 15 inches of water may be achieved. This pressure increase may be used to overcome pressure drop and facilitate proper mixing (described below) of cooler air with the exhaust gas stream 32 in the downstream exhaust processing system 14. The pressure increase may also be used to supercharge the gas turbine system 12.

Referring to FIGS. 1 and 3, an air extraction system 70 may be employed to extract at least some of the additional flow of air provided by the fan 58 (e.g., any airflow greater than the flow rate capacity of the compressor component 18 of the gas turbine system 12). A flow of air 72 may be extracted using, for example, one or more extraction ducts 74 (FIG. 3). The extracted air, or “bypass air” (BA) does not enter the gas turbine system 12, but is instead directed to the mixing area 33 through the bypass ducts 76 as indicated by arrows BA, where the bypass air may be used to cool the exhaust gas stream 32. The remaining air (i.e., any portion of the additional flow of air not extracted via the extraction ducts 74) enters the compressor component 18 of the gas turbine system 12 and flows through the gas turbine system 12 in a normal fashion. If the flow of remaining air is greater than the flow rate capacity of the compressor component 18 of the gas turbine system 12, a supercharging of the gas turbine system 12 may occur, increasing the efficiency and power output of the gas turbine system 12.

The bypass air may be routed toward the mixing area 33 downstream of the turbine component 22 through one or more bypass ducts 76. The bypass air exits the bypass ducts 76 and enters the mixing area 33 through a bypass air injection grid 110 (FIG. 1), where the bypass air (e.g., ambient air) mixes with and cools the exhaust gas stream 32 to a temperature suitable for use with the SCR catalyst 38. In embodiments, the temperature of the exhaust gas stream 32 generated by the gas turbine system 12 is cooled by the bypass air from about 1100° F. to less than about 900° F. in the mixing area 33. The bypass air injection grid 110 (FIG. 1) may comprise, for example, a plurality of nozzles 112 or the like for directing (e.g., injecting) the bypass air into the mixing area 33. The nozzles 112 of the bypass air injection grid 110 may be distributed about the mixing area 33 in such a way as to maximize mixing of the bypass air and the exhaust gas stream 32 in the mixing area 33. The nozzles 112 of the bypass air injection grid 110 may be fixed in position and/or may be movable to selectively adjust the injection direction of bypass air into the mixing area 33.

A supplemental mixing system 78 (FIG. 1) may be positioned within the mixing area 33 to enhance the mixing process. The supplemental mixing system 78 may comprise, for example, a static mixer, baffles, and/or the like. The CO catalyst 36 may also help to improve the mixing process by adding back pressure (e.g., directed back toward the turbine component 22).

As depicted in FIG. 3, the air flow into each extraction duct 74 may be selectively controlled using a flow restriction system 80 comprising, for example, a damper 82, guide vane, or other device capable of selectively restricting airflow. Each damper 82 may be selectively controlled (e.g., rotated) by an independent actuator 84. The actuators 84 may comprise electro-mechanical motors, or any other type of suitable actuator. The dampers 82 may be independently and/or collectively controlled in response to commands from the airflow controller 100 to selectively vary the positioning of the dampers 82 such that a desired amount of bypass air is directed into the mixing area 33 via the bypass ducts 76. Position information (e.g., as sensed by electro-mechanical sensors or the like) for each of the dampers 82 may be provided to the airflow controller 100.

Bypass air may be selectively released from one or more of the bypass ducts 76 using an air release system 86 comprising, for example, one or more dampers 88 (or other devices capable of selectively restricting airflow, e.g. guide vanes) located in one or more air outlets 90. The position of a damper 88 within an air outlet 90 may be selectively controlled (e.g., rotated) by an independent actuator 92. The actuator 92 may comprise an electro-mechanical motor, or any other type of suitable actuator. Each damper 88 may be controlled in response to commands from the airflow controller 100 to selectively vary the positioning of the damper 88 such that a desired amount of bypass air may be released from a bypass duct 76. Position information (e.g., as sensed by electro-mechanical sensors or the like) for each damper 88 may be provided to the airflow controller 100. Further airflow control may be provided by releasing bypass air from one or more of the bypass ducts 76 through one or more metering valves 94 controlled via commands from the airflow controller 100.

The airflow controller 100 (FIG. 1) may be used to regulate the amount of air generated by the fan 58 that is diverted as bypass air into the mixing area 33 through the bypass ducts 76 relative to the amount of air that enters the gas turbine system 12 (and exits as the exhaust gas stream 32) in order to maintain a suitable temperature at the SCR catalyst 38 under varying operating conditions. A chart showing an illustrative relationship between the flow of bypass air into the mixing area 33 and the temperature of the exhaust gas stream 32 at different load percentages of the gas turbine system 12 is provided in FIG. 4. In this example, the chart in FIG. 4 depicts: 1) temperature variation of an exhaust gas stream 32 of a gas turbine system 12 at different load percentages of the gas turbine system 12; and 2) corresponding variation in the flow of bypass air as a percentage of the exhaust gas stream 32 (bypass ratio) needed to maintain the temperature at the SCR catalyst 38 at a suitable level (e.g., 900° F.) at different load percentages of the gas turbine system 12. As represented in the chart in FIG. 4, the amount of bypass air flowing through the bypass ducts 76 into the mixing area 33 may be varied (e.g., under control of the airflow controller 100) as the temperature of the exhaust gas stream 32 changes, in order to regulate the temperature at the SCR catalyst 38.

The airflow controller 100 (FIG. 1) may receive data 102 associated with the operation of the gas turbine power generation system 10. Such data may include, for example, the temperature of the exhaust gas stream 32 as it enters the mixing area 33, the temperature of the exhaust gas stream 32 at the SCR catalyst 38 after mixing/cooling has occurred in the mixing area 33, the temperature of the air drawn into the air intake section 16 by the combined action of the fan 58 and the compressor component 18 of the gas turbine system 12, and other temperature data obtained at various locations within the gas turbine power generation system 10. The data 102 may further include airflow and pressure data obtained, for example, within the air intake section 16, at the inlet guide vanes 66, at the fan 58, at the entrance of the compressor component 18, within the extraction ducts 74, within the bypass ducts 76, at the downstream end 30 of the turbine component 22, and at various other locations within the gas turbine power generation system 10. Load data, fuel consumption data, and other information associated with the operation of the gas turbine system 12 may also be provided to the airflow controller 100. The airflow controller 100 may further receive positional information associated with the inlet guide vanes 66, dampers 82 and 88, valve 94, etc. It should be readily apparent to those skilled in the art how such data may be obtained (e.g., using appropriate sensors, feedback data, etc.), and further details regarding the obtaining of such data will not be provided herein.

Based on the received data 102, the airflow controller 100 is configured to vary as needed the amount of bypass air flowing through the bypass ducts 76 into the mixing area 33 to maintain the temperature at the SCR catalyst 38 at a suitable level. This may be achieved, for example, by varying at least one of: the flow of air drawn into the air intake section 16 by the combined action of the fan 58 and the compressor component 18 of the gas turbine system 12 (this flow may be controlled, for example, by adjusting the position of one or more of the inlet guide vanes 66 and/or by increasing the rotational speed of the shaft 24); the flow of air 72 into the extraction ducts 74 (this flow may be controlled, for example, by adjusting the position of one or more of the dampers 82); and the flow of bypass air passing from the extraction ducts 74, through the bypass ducts 76, into the mixing area 33 (this flow may be controlled, for example, by adjusting the position of one or more of the dampers 88 and/or the operational status of the metering valves 94).

The airflow controller 100 may include a computer system having at least one processor that executes program code configured to control the amount of bypass air flowing through the bypass ducts 76 into the mixing area 33 using, for example, data 102 and/or instructions from human operators. The commands generated by the airflow controller 100 may be used to control the operation of various components (e.g., such as actuators 68, 84, 92, clutch mechanism 62, valve 94, and/or the like) in the gas turbine power generation system 10. For example, the commands generated by the airflow controller 100 may be used to control the operation of the actuators 68, 84, and 92 to control the rotational position of the inlet guide vanes 66, dampers 82, and dampers 88, respectively. Commands generated by the airflow controller 100 may also be used to activate other control settings in the gas turbine power generation system 10.

The use of an airflow generation system 56 including a fan 58 in lieu of conventional large external blower systems and/or other conventional cooling structures provides many advantages. For example, the need for redundant external blower systems and associated components (e.g., blowers, motors and associated air intake structures, filters, ducts, etc.) is eliminated. This reduces manufacturing and operating costs, as well as the overall footprint, of the gas turbine power generation system 10. The footprint is further reduced as the fan 58 draws in air through an existing air intake section 16, rather than through separate, dedicated intake structures often used with external blower systems.

Use of the fan 58 provides a more reliable and efficient gas turbine power generation system 10. For example, since the bypass air used for cooling in the mixing area 33 is driven by the shaft 24 of the gas turbine system 12 itself, large external blower systems are no longer required. Further, at least a portion of the flow of air generated by the fan 58 may be used to supercharge the gas turbine system 12.

Power requirements of the gas turbine power generation system 10 are reduced because the fan 58 is coupled to, and driven by, the shaft 24 of the gas turbine system 12. This configuration eliminates the need for large blower motors commonly used in conventional external blower cooling systems.

In various embodiments, components described as being “coupled” to one another can be joined along one or more interfaces. In some embodiments, these interfaces can include junctions between distinct components, and in other cases, these interfaces can include a solidly and/or integrally formed interconnection. That is, in some cases, components that are “coupled” to one another can be simultaneously formed to define a single continuous member. However, in other embodiments, these coupled components can be formed as separate members and be subsequently joined through known processes (e.g., fastening, ultrasonic welding, bonding).

When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element, it may be directly on, engaged, connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. An airflow control system for a gas turbine system, comprising: an airflow generation system for attachment to a rotatable shaft of a gas turbine system, the airflow generation system drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream of the gas turbine system; and an air extraction system for extracting at least a portion of the excess flow of air generated by the airflow generation system to provide bypass air, and for diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream.
 2. The airflow control system of claim 1, wherein the airflow generation system comprises a fan.
 3. The airflow control system of claim 2, further comprising at least one inlet guide vane for controlling a flow of air through the fan.
 4. The airflow control system of claim 2, wherein the fan is fixedly coupled to the shaft or releasably coupled to the shaft using a clutch mechanism.
 5. The airflow control system of claim 1, further comprising a mixing system for mixing the bypass air with the exhaust gas stream in the mixing area.
 6. The airflow control system of claim 1, wherein the air extraction system further comprises a bypass duct for diverting the bypass air around the gas turbine system into the mixing area to reduce the temperature of the exhaust gas stream in the mixing area.
 7. The airflow control system of claim 6, further comprising a flow restriction system coupled to the bypass duct for selectively restricting the amount of bypass air flowing into the bypass duct.
 8. The airflow control system of claim 1, wherein the excess flow of air drawn in by the airflow generation system comprises about 10 percent to about 40 percent of a flow of air drawn in by a compressor component of the gas turbine system.
 9. The airflow control system of claim 1, wherein the air extraction system is configured to divert any non-extracted portion of the excess flow of air into a compressor component of the gas turbine system to supercharge the gas turbine system.
 10. The airflow control system of claim 1, further comprising a selective catalytic reduction (SCR) system for processing the reduced temperature exhaust gas stream.
 11. The airflow control system of claim 1, further comprising an airflow controller for controlling the air extraction system to maintain the reduced temperature exhaust gas stream at a temperature of less than about 900° F.
 12. A turbomachine system, comprising: a gas turbine system including a compressor component, a combustor component, and a turbine component; a shaft driven by the turbine component; a fan coupled to the shaft upstream of the gas turbine system for drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream produced by the gas turbine system; an air extraction system for: extracting at least a portion of the excess flow of air generated by the fan to provide bypass air; and diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream; an airflow controller for controlling the air extraction system to maintain the reduced temperature exhaust gas stream at a temperature of less than about 900° F.; and a selective catalytic reduction (SCR) system for processing the reduced temperature exhaust gas stream.
 13. The turbomachine system of claim 12, further comprising at least one inlet guide vane for controlling a flow of air through the fan, each inlet guide vane coupled to an actuator configured to rotate the inlet guide vane.
 14. The turbomachine system of claim 12, wherein the fan is either fixedly coupled to the shaft or releasably coupled to the shaft using a clutch mechanism.
 15. The turbomachine system of claim 12, further comprising a mixing system for mixing the bypass air with the exhaust gas stream in the mixing area.
 16. The turbomachine system of claim 12, wherein the air extraction system further comprises a bypass duct for diverting the bypass air around the gas turbine system into the mixing area to reduce the temperature of the exhaust gas stream in the mixing area.
 17. The turbomachine system of claim 16, further comprising a flow restriction system coupled to the bypass duct for selectively restricting the amount of bypass air flowing into the bypass duct.
 18. The turbomachine system of claim 12, wherein the excess flow of air drawn in by the airflow generation system comprises about 10 percent to about 40 percent of a flow of air drawn in by the compressor component.
 19. The turbomachine system of claim 12, wherein the air extraction system is configured to divert any non-extracted portion of the excess flow of air into the compressor component of the gas turbine system to supercharge the gas turbine system.
 20. A power generation system, comprising: a gas turbine system including a compressor component, a combustor component, and a turbine component; a shaft driven by the turbine component; an electrical generator coupled to the shaft for generating electricity; a fan coupled to the shaft upstream of the gas turbine system for drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream produced by the gas turbine system; an air extraction system for: extracting at least a portion of the excess flow of air generated by the can to provide bypass air; and diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream; an airflow controller for controlling the air extraction system to maintain the reduced temperature exhaust gas stream at a temperature of less than about 900° F.; and a selective catalytic reduction (SCR) system for processing the reduced temperature exhaust gas stream. 